The present invention relates in general to a latch for lockably retaining a door in a fully closed position, and in particular to a mechanism for inhibiting the locking movement of the latch when the door is not properly positioned to effect its locking.
The invention finds particular use as a safety device for a domestic range having a self-cleaning oven of the pyrolytic type. Such a range may also include a microwave energy source for irradiating food placed in the oven cavity that typically contains conventional resistance heating elements. This "common cavity" type oven enables a user to cook food therein with microwave energy only or with conventional resistance heating only, or with a combination of both. Also, the resistance heating elements can be used to highly heat the oven cavity to effect a pyrolytic cleaning action of the walls thereof.
It is imperative for recognized safety reasons that an associated oven door remain locked in a fully closed position during periods of microwave irradiation in the oven or during a high temperature pyrolytic oven cleaning cycle. While a microwave energy source can quickly be disabled by microswitches sensing the unlocking of the door, thus avoiding an unsafe "open-door" operating condition, the pyrolytic cleaning action of a highly heated oven cannot be so readily terminated. Thus, it is further necessary to prevent the unlocking of the oven door by the user during the period of time that the oven cavity is at a pyrolytic cleaning temperature, since premature unlocking and opening of the door could expose the user to very high temperature pyrolytic-induced oven gases and could also result in an explosion of such gases if they are combustible, as is often the case when a very dirty oven is being pyrolytically cleaned.
In view of the above safety requirements, it is known to provide such a "common cavity" type self-cleaning oven with a three-position, manually actuated oven door latch mechanism. At a first or unlocked position, the latch mechanism permits free opening and closing of the oven door for conventional baking and broiling within the oven. At a second or microwave position, the latch mechanism locks the door at a closed position during a microwave cooking cycle, the user being able at any time to move the latch mechanism from its second to its first position to terminate the microwave cooking cycle and unlock and open the oven door. A plurality of interlock-type microswitches actuated by the latch mechanism only at its second position enable the microwave circuitry. At a third or pyrolytic cleaning position, the latch mechanism locks the oven door in a closed position. Further, another interlock-type microswitch, only responsive to the movement of the door latch to its third position, enables the self-cleaning circuitry to energize the oven heating elements. Further, a temperature-controlled retaining mechanism prevents unlocking of the oven door by the user when the oven temperature is at a pyrolytic or near pyrolytic level.
It can be seen that the various interlock switches are responsive to movement of the latch mechanism and not to movement of the oven door itself. It thus becomes absolutely necessary to ensure that the latch mechanism cannot be moved to a locked position, i.e., its second or third position, without its proper engagement with the oven door. In other words, a fail-safe device must be provided to ensure that a user cannot inadvertently energize the range into a microwave or self-cleaning cycle without proper locking of the oven door at its closed position.